Companies and organizations operate computer networks that interconnect numerous computing systems to support their operations. The computing systems can be located in a single geographical location (e.g., as part of a local network) or located in multiple distinct geographical locations (e.g., connected via one or more private or public intermediate networks). Data centers can house significant numbers of interconnected computing systems, such as, e.g., private data centers are operated by a single organization and public data centers operated by third parties to provide computing resources to customers. Public and private data centers can provide network access, power, hardware resources (e.g., computing and storage), and secure installation facilities for hardware owned by the data center, an organization, or by other customers.
To facilitate increased utilization of data center resources, virtualization technologies can allow a single physical computing machine to host one or more instances of virtual machines that appear and operate as independent computer machines to a connected computer user. With virtualization, the single physical computing device can create, maintain or delete virtual machines in a dynamic manner. In turn, users can request computer resources from a data center and be provided with varying numbers of virtual machine resources on an “as needed” basis or at least on an “as requested” basis.
While virtualization can make available a large number of running virtual machine instances, the task of managing system resources such as volatile memory (e.g., random access memory (RAM)) allocated to those instances involves a balancing of the goals of performance guarantees (e.g., according to service level agreements (SLAs)) and efficient resource allocation.